Injection Technique: IM, IV and Subcutaneous Without Complications

This article describes the principles behind safe injection practice. Administering prescription veterinary medicines is a task for a veterinarian or for trained personnel working under veterinary direction — the point of writing it down is so that the people doing it understand why the steps exist.

Route is not interchangeable

The route on the label is part of the formulation, not a suggestion. Getting it wrong causes specific, predictable harm:

• Phenylbutazone given perivascularly instead of intravenously causes severe tissue necrosis and sloughing
• Procaine penicillin given intravenously causes acute procaine reaction — excitement, collapse, sometimes death
• Oily preparations given intravenously cause pulmonary embolism
• Vitamin K1 given intravenously causes anaphylactoid reactions and has killed horses
• Long-acting oxytetracycline given intravenously causes cardiovascular collapse

Every one of these is on a label somewhere and every one of them still happens.

The four errors

1. Not aspirating. Draw back on the plunger before injecting anything intramuscularly. Blood in the hub means the needle is in a vessel — withdraw, redirect, aspirate again. This single step prevents the procaine reaction.

2. Injecting through dirt. The needle carries whatever is on the skin into the muscle. Clean the site, let it dry, use a fresh needle to draw and a fresh needle to inject, and never re-enter a vial with a used needle.

3. Too much volume in one site. Intramuscular volumes above 10–15 ml in a horse should be split across sites. Large single volumes cause pressure, pain and swelling, and irritant products make it worse.

4. Reusing needles across animals. This is how an abscess outbreak starts on a yard, and it is entirely avoidable.

Site selection in the horse

Intramuscular. The neck (in the triangle bounded by the nuchal ligament, cervical vertebrae and scapula), the pectorals, and the semitendinosus/semimembranosus. Rotate sites and keep a record — the same site used repeatedly gets sore and fibrotic.

Intravenous. The jugular groove, upper third, needle directed downward with the vein raised. The carotid artery lies deep to the jugular; injecting a drug intended for the vein into the artery sends it straight to the brain, and the consequences are immediate and severe. If blood pulses rather than flows, withdraw.

Subcutaneous. Less used in horses; the loose skin of the neck and shoulder where the label calls for it.

Camels

Camel skin is thicker and tougher than equine skin, particularly over the neck. Practical differences:

• Longer, larger-gauge needles are usually required
• The jugular is accessible but the skin over it is dense — expect more resistance
• Restraint is different. A sitting camel is a different proposition to a standing one, and handler safety comes first
• Volumes are often larger, which makes site-splitting more important, not less

Aftercare

Record every injection: date, time, product, batch number, dose, route, site, and who gave it. This serves clinical follow-up and it serves you at a stewards' enquiry.

Check injection sites at 24 and 48 hours. Investigate promptly:

• Heat, pain or swelling that is increasing rather than settling
• Any discharge
• Lameness after a hindquarter injection
• Fever

Clostridial myositis following intramuscular injection progresses in hours, not days, and is fatal without immediate aggressive treatment. It is the reason several products are labelled intravenous-only in horses.

A yard where injection sites are checked and recorded catches the rare disaster early. A yard where they are not finds out when the animal is severely ill.